1. Field of the Invention
This invention relates generally to environmental control systems such as heating, ventilating, humidifying and air-conditioning systems, and more particularly to an environmental control system providing independent operation, and convenient control of the humidifier using existing wiring.
2. Description of the Prior Art
Humidification of the living space in the household is desirable because static shocks and the drying of respiratory tracks occurs if the humidity level is low. However, humidification does not always occur at the most desirable times with known systems.
Conventional household heating, ventilating and air-conditioning (HVAC) systems such as are shown in U.S. Pat. Nos. 2,544,544, 3,587,558 and 3,877,459 operate using forced air and include a humidifier slaved to the system's blower fan. The blower is dependent upon the operation of the furnace component or the air-conditioning component of the system, and humidification only occurs when the household temperature is being adjusted. Furthermore, when the outside air temperature and the thermostat setting for the inside air temperature in the HVAC system are approximately the same, the furnace, and consequently the humidifier, will rarely activate and a condition of low humidity cannot be corrected.
Further disadvantages result from slaving the humidifier to the system blower. Moisture in a living space retains heat and tends to maintain the temperature in the living space. If the humidifier only operates when the furnace adjusts the air temperature of the living space, the humidity in the living space is less than optimum and consequently the retention of heat in the living space is also less than optimum. Additionally, a humidifier can add moisture to a living space which is dry and hot so that the moisture absorbs heat and thereby reduce air temperature while providing moisture to the air.
Accordingly, there are strong advantages to an environmental control system having a humidifier which operates independently of the heating and cooling elements.
U.S. Pat. Nos. 3,305,173 and 4,186,873 disclose prior art solutions to the problem of providing independent humidifier control. U.S. Pat. No. 3,305,173 discloses a six wire system for controlling a blower and a furnace from a living area. However, existing HVAC systems are traditionally controlled by four wires extending from the environmentally controlled living area to the plant area where the humidifier, furnace and air-conditioner are usually located. The application of the system shown in U.S. Pat. No. 3,305,173 to an existing environmental control system requires the rewiring of the household to include at least two more connecting wires to provide independent humidifier control, and even more additional wires if an air-conditioner is included in the system.
U.S. Pat. No. 4,186,873 avoids the rewiring the household by adding a household carrier current transmitter to the living space and a household carrier current receiver to the plant area. However, carrier current control can significantly raise the cost of a household environmental control system as well as interfere with existing household carrier current security systems or the like.